Re: Any more graceful way to saturate adds?

aku ankka wrote:
> Hello. You can use carry to generate a saturation mask. The idea
> revolves around this concept:
> 
> 0 - 1 = -1 (all bits set)
> 0 - 0 = 0
> 
> add al, bl ; this is ur addition
> xor cl, cl ; zero d cl register

This XOR will overwrite the flags from the previous ADD!
INC/DEC are the only arithmetic opcodes which doesn't modify the carry
flag.

> sbb cl, cl ; cl = cl - cl - carry = 0 - 0 - carry = 0 - carry
> or  al, cl ; this will saturate; the cl = 0xff if carry was set.. else
> it is 0x00
> 
> w00t++ w00t++
> 
> Saturating w/o branching is child's play; enjoy!

Children often make simple mistakes. :-)

Terje

-- 
- <Terje.Mathisen@[EMAIL PROTECTED]
>
"almost all programming can be viewed as an exercise in caching"